They claim that various provisions of the state law "prohibit some plaintiffs from performing the duties required of them by the Affordable Care Act (ACA), prohibit other plaintiffs from providing information about health insurance altogether, and prevent plaintiffs and the Missouri public from receiving information about health insurance from the person or source of their choosing."

The plaintiffs say the Missouri law has made their work pretty much impossible. You can read the complaint here.

"Missouri has placed groups like St. Louis Effort for AIDS in an untenable situation: If they comply with Missouri statutes, they can't perform the duties the Affordable Care Act requires them to perform, but if they comply with the ACA and do perform those duties, they violate the Missouri law and are subject to thousands of dollars in penalties for doing so," says Jay Angoff of Mehri and Skalet, who is representing the plaintiffs. Angoff is a former Missouri insurance commissioner and also the former head of the federal office implementing the ACA at the Department of Health and Human Services.